As discussed in a research paper, Telecommunications Society, Magnetic Recording Research Group, research data MR67-18 (1967), pages 1 to 16, the magnetic properties of longitudinal magnetic recording media are defined by the thickness t.sub.m of the recording medium, the coercive force in the direction of travel of the magnetic head, the remanence magnetization M.sub.r, and the square ratio S.sub.q (S.sub.q =M.sub.r /M.sub.s where M.sub.s is the saturation magnetization).
IEEE Transaction on Magnetics, MAG-20, No. 1, JANUARY 1984, pages 81 to 83, proposes various symbols such as an S* representing an inclination of magnetization curve for the coercive force, S' representing an inclination of magnetization curve for the remanence coercive force in the remanence magnetization curves, a value .DELTA.h.sub.c obtained by normalizing the full-width at half maximum h.sub.c of the differential magnetization curve by the coercive force, and a value .DELTA.h.sub.r obtained by normalizing the full-width at half maximum h.sub.r of the differential magnetization curve by the remanence coercive force. These properties are defined as shown by the diagram in FIG. 1. In FIG. 1, symbol M indicates an amplitude of magnetization, H an applied magnetic field, H.sub.r a remanence coercive force, and H.sub.s an intensity of the applied magnetic field in the major loop of hysteresis at which the magnetization produced when the applied magnetic field increases begins to match or separate from the magnetization produced when the applied magnetic field decreases.